1. Field of the Invention
The present invention relates to a rotary compressor, and, in particular, to a rotary compressor wherein the sound resulting from the pressure pulsations of the discharge gas discharged from between the bearing and the silencer cover which covers the bearing is efficiently reduced.
2. Description of the Related Art
Generally, the pressurizing element of a rotary compressor, which has been adopted for a cooling cycle and the like, mainly comprises a cylinder, a main bearing, an auxiliary bearing, a rotating shaft, a roller, and a blade. The compressor is driven by the rotation of the rotary shaft which is connected to a transmission element provided in its upper part. The rotary shaft is supported by the main bearing and the auxiliary bearing, and the main bearing and the auxiliary bearing cover the upper side and the lower side of an annular cylinder, in which a compression space is formed. Within this compression space, the roller is provided in an eccentric shaft portion of the rotary shaft and rolls against the inner wall of the cylinder. The interior of the compression section is divided into a high pressure side and a low pressure side by a blade which is provided in a freely sliding manner on the cylinder in contact with the roller.
For this type of rotary compressor, both an auxiliary bearing discharge type and a main bearing discharge type are known. Specifically, a discharge port is provided in the main bearing or in the auxiliary bearing, and this port communicates with the high pressure side in the compression space. A discharge valve or a check valve is provided in this discharge port.
One end of the discharge valve is secured to the bearing, while the other end, which is the free end, is seated on the discharge port and acts to seal this port. When the pressure inside the compression space becomes higher than a set pressure, the free end of the discharge valve draws away from the discharge port and the compressed gas is discharged. Accordingly, a discharge noise is developed, caused by the discharge gas.
Generally, if the frequency of the noise from a rotary compressor is analyzed, it is found to have three modes. These are the 100 to 500 Hz low frequency sound, made up of the vibration sound from the rigid body of the compressor and electromagnetic sound, the 630 Hz to 2 KHz medium frequency sound, and the high frequency sound above 2.5 KHz. Among these, the medium frequency sound is the most obvious, so that it is desirable to suppress the sound from the discharged gas in this frequency range.
Accordingly, in order to suppress this sound from the discharge gas, the provision of various devices such as a sound suppression cover with a vent which covers the discharge port and discharge valve has been adopted.
The sound supression cover is also referred to as a valve cover or a discharge cover.
For example, in the Japanese Patent Publication of Unexamined Application No. SHO-59-43996, a discharge orifice is provided at the side of the discharge port to alleviate the force of the shock received by the valve seat when the discharge valve is closed. Also, in the Japanese Patent Publication of Unexamined Application No. SHO-57-23796, the speed of closure of the discharge valve is adjusted, using a guide element, to cushion the shock received by the valve seat when the valve is closed. In both of these cases the sound in the high frequency range caused by the shock to the discharge valve is suppressed.
Next, the cause of development of medium frequency noise is considered to be the pressure pulsations produced within the sound suppression cover which covers the discharge valve. To suppress the noise caused by this type of pressure pulsations, for example, in the Japanese Patent Publication of Unexamined Application No. SHO-59-46383, a tubular body for suppression of sound is provided as a side branch type sound suppressor in a discharge chamber formed in the space between the sound suppression cover and the bearing. In addition, in the Japanese Utility Model Publication of Unexamined Application No. SHO-58-46880, there is provided a tubular body or a cavity section with a bottom which opens into a discharge chamber formed from a sound suppression cover of the type provided on the bearing as previously described. The same type of cavity section is disclosed in the Japanese Patent Publication of Unexamined Application No. SHO-59-105980.
These publications are incorporated into the present specification by reference.
In the conventional structure of these examples, the cavity section with bottom for the side branch type of sound suppression opens into the discharge chamber at a position offset by 180 degrees from the position of the discharge port. Because of this, the phase of the pressure pulsations produced within the discharge chamber is reversed, so that the pressure vibrations produced in the discharge chamber are offset and the sound is suppressed or attenuated. This configuration is based on the following considerations.
Specifically, for the pressure pulsations when the compressed gas is discharged from the discharge port, at a certain instant, half of the region of that discharge port side in the annular discharge chamber becomes a positive pressure wave region. As opposed to this, half of the region of the opposite side offset at an angle of 180 degrees to that discharge port becomes a negative pressure wave region. Then, in the next instant, the plus and minus pressure pulsations reverse. This produces a pressure pulsation standing wave. Accordingly, the cavity section with bottom may be placed anywhere within the discharge chamber, but mainly, to improve ease of processing or installation, it is placed at 180 degrees from the discharge port. However, with this configuration, effective suppression of the pulsations is not adequately obtained. Accordingly, it is believed that further improvement is required in the setting of the conventional cavity section with bottom.